The present invention relates to a linear encoder for detecting the positions of a table and the like of a machine tool, which table and the like moving linearly and for outputting position data of the positions detected.
Nowadays, in general, the conventional linear encoders of an optical type and a magnetic type have been used to detect the linear positions of a machine tool part.
The conventional linear encoder which is used commonly maybe an optical type or a magnetic type as shown in FIG. 1 and comprises a table 3 driven by the driving of a drive shaft 5 in the directions shown by the arrows, a main scale 1 having a gradation of information used as a standard of position and having its longitudinal axis arranged in parallel with a moving direction of the table 3, a slider 2 fixed to the table 3 so as to move together with the table 3 in order to read the information on the main scale 1, and to convert the information into an electrical signal S, and to output it, and a signal processor 4 for converting the electrical signal S sent from the slider 2 into position data P.sub.OSD and for outputting the position data.
It is necessary to lengthen the main scale of the conventional linear encoder, when the movement stroke of the table lengthens, in order to match with the lengthened stroke above. However, it is understood that precisely manufacturing the main scale in a form of one long member necessitates a very large manufacturing installation of high cost. Still more, the size of the manufacturing installation for the long main scale has a restriction, so that the length of the main scale manufactured by the installation has a limit. Accordingly, when it is necessary to manufacture very long main scale exceeding the restriction in length, a bonding or binding agent is used to joint two main scales, thereby obtaining a single long scale. It is noted that the jointing procedure of two scales necessitates many troublesome working steps, resulting in poor precision of such a jointed main scale.